[!824] Remove deprecated FindUMFPack.cmake module

Merge branch 'issue/remove_find_umfpack' into 'master'

ref:core/dune-common\>

### Summary

This MR removed the deprecated FindUMFPack module. Its functionality is
replaced by FindSuiteSparse

Closes [#208]

See merge request [!824]

  [#208]: gitlab.dune-project.org/NoneNone/issues/208
  [!824]: gitlab.dune-project.org/core/dune-common/merge_requests/824


Closes #208